For a user with healthy eyes, when he views a small object or an object far from him, the eyes hardly observe desired details. For example, when people sitting at a relatively distant location watch a ball game, they hardly observe details of body movement and expression of athletes. For a user with an eye problem such as myopia or hyperopia, when he views a small object or an object far from him, it is more difficult to recognize details of the observed object or people. Conversely, when a user views a large object or an object near him, the user hardly observes global information of the gazed object. For example, when a user stands in front of a tall building or a mountain, he hardly observes the overall situation.
A traditional optical zoom device, such as a telescope or a magnifying glass, is not convenient to use because zooming parameters are required to be set manually.